Patent GB-1172991-A (GB)
Title: Improvements in or relating to Telephone Systems
Inventor: BROWELL LESLI JAMES
IPC: H04Q3/00
Filed: 1966-03-29
Abstract: 1,172,991. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 13 March, 1967 [29 March, 1966], No. 13921/66. Heading H4K. In a register controlled exchange, in order that sending should not overtake the digits made available by dialling, an inspection of the initial digits of a dialled number is made to determine the number of digits that shall be received before a junction circuit is seized. If loop disconnect pulses are sent a junction is seized before all the digits have come in, but if multi-frequency sending is employed all the digits are collected first. The invention is described in the context of a cross-bar system the routing section of which is shown in Fig. 1. Trunks OT from twenty two-stage line distributers each serving 500 subscribers are connected over distribution frame TDF to the twostage router R where they terminate on local relay groups LTRG. Incoming junctions terminated on relay groups ITRG are similarly distributed over TDF. The relay groups are served by registers LREG and IREG which work to a common router control RC. Outlets from the router are split into a group TT for locally terminated calls and a group giving access to outgoing junctions OJI to OJN. Router control RC employs marker LMKR for local calls and a marker JMKR for tandem calls and local calls outgoing over junctions. Outgoing calls involve a coder CDR to determine required routes, class of service, and tariff. Senders SDR of various signalling type provide digit storage for digits in excess of the seven digits capacity of the registers. Received digits are stored in 2-out-of-5 code except in the coder CDR where they have decimal form. Given digits in a register sufficient to indicate an outgoing call the control RC calls in coder CDR. If more digits are required to determine a route the coder and control release and instruct the register to call again. Given sufficient digits the coder CDR supplies instructions to set up marker JMKR. The above process is subject to delay according to the first one, two, three or four digits. It is said that the fifth digit may also be taken into account. As shown in Figs. 2 and 3, which connect side-by-side, the register REG has a store DS for digits 1D to 7D, a number of digits received counter NDR (1-7) operating respective relays NDR1 to NDR7. The first digit is inspected by a decoder to code point expansion tree DET, the code points being strapped to leads 2C to 10C. As shown, initial digits 1 or 2 cause a mark on lead 7c causing register ND to record that seven digits are to be expected. With a mark on lead ND7 of register ND a relay AD is operated to disable test circuit TC so that the register cannot call in router control RC until digits received counter NDR has operated relays NDR1 to NDR7 in succession. When AD falls back to sanction connection to control RC, five digits are transferred and routing proceeds. Initial digit O is shown as marking lead 10c to disconnect the test circuit until the tenth digit. Since digits 8, 9 and 10 are received in the sender SDR a digits received counter NDR (8-10) in the sender controls the relays NDR8 to NDR10 which hold relay AD over sender connector contacts SC. If discrimination for delay cannot be made on the first digit the router control RC is brought in to test the first two digits over a decoder expansion tree DET the code points of which are strapped to leads 3c to 10c. If two digits produce no result the control RC releases and is taken into use again when the third digit is available to see if discrimination can be based on three digits. If two or three digits effect discrimination the number of digits to be expected is recorded in store ND in register REG to operate AD. Relay CO operates in control RC to release the control while AD prevents its reseizure until all digits are in. If the control RC fails to discriminate its test circuit TC brings in the coder CDR which examines three digit codes for which RC is not equipped and, if necessary, is called in again to examine four digit codes. As the digits in CDR are in decimal form, code point markings are established from an expansion tree ET. Code points are strapped to leads 4C to 10C to set up register ND in register REG and to consequently operate relays CO and AD as before in the case of control RC.